As an electrically rewritable nonvolatile semiconductor memory device that can be formed with high integration density, a NAND flash memory is known. The NAND flash memory includes a plurality of blocks each of which is the minimum unit of data erase. Each block includes a plurality of NAND strings each having a plurality of memory cells serially connected by forming every adjacent two of the memory cells to commonly have one of source and drain regions and both ends of each NAND string are respectively connected to bit and source lines via select gate transistors.
Each memory cell of the NAND flash memory includes a floating gate electrode formed above a semiconductor substrate with a tunnel insulating film disposed therebetween and a control gate electrode formed above the floating gate electrode with an intergate insulating film disposed therebetween and stores data in a nonvolatile fashion by utilizing variation in the threshold voltage depending on the amount of charges stored in the floating gate electrode.